1. Field of the Invention
The present invention relates to a method of fabricating a piezoelectric vibrating piece, a piezoelectric vibrating piece fabricated by the fabricating method, a wafer used for fabricating the piezoelectric vibrating piece, a piezoelectric vibrator having the piezoelectric vibrating piece, an oscillator, an electronic apparatus and a radiowave timepiece having the piezoelectric vibrating piece.
2. Description of the Related Art
In recent years, a portable telephone or a portable information terminal apparatus uses a piezoelectric vibrator utilizing quartz or the like as a time source, a timing source of a control signal or the like or a reference signal source or the like. As a piezoelectric vibrator of this kind, various ones are known, for example, a piezoelectric vibrator having a piezoelectric vibrating piece of a tuning fork type, a piezoelectric vibrator having a piezoelectric vibrating piece of carrying out a thickness slipping vibration and the like are known.
Explaining by taking an example of a piezoelectric vibrating piece of a tuning fork type, as shown by FIG. 22 and FIG. 23, a piezoelectric vibrating piece 201 includes a piezoelectric plate 212 having a pair of vibrating arm portions 210 arranged in parallel and a base portion 211 integrally fixing base end sides of the pair of vibrating arm portions 210, a pair of exciting electrodes 213 formed on outer surfaces of the pair of vibrating arm portions 210 for vibrating the pair of vibrating arm portions 210, and mount electrodes 214 respectively electrically connected to the pair of exciting electrodes 213. When a predetermined drive voltage is applied to the pair of exciting electrodes 213 by way of the pair of mount electrodes 214, the piezoelectric vibrating piece 201 is vibrated in directions of making the pair of vibrating arm portions 210 proximate to or remote from each other. Further, at this occasion, weights of weight metal films 215 coated to front ends of the vibrating arm portions 210 are previously adjusted (frequency adjustment) such that the pair of vibrating arm portions 210 are vibrated by a predetermined frequency.
It is general to fabricate a plurality of the piezoelectric vibrating pieces 201 of this kind at a time utilizing a wafer made of various piezoelectric materials of quartz, lithium tantalate, lithium niobate or the like (for example, JP-A-7-212161.
Specifically, as shown by FIG. 24, after constituting a wafer S by cutting a raw stone of a piezoelectric material, the wafer S is polished to a predetermined thickness. Further, the respective electrodes and the weight metal film 215 are formed by cleaning and drying the polished wafer S, forming an outer shape of the piezoelectric plate 212 by working the wafer S by etching by photolithography technology and patterning a predetermined metal film. Thereafter, a plurality of the piezoelectric vibrating pieces 201 can be fabricated at a time from the single wafer S by cutting to fragment the respective piezoelectric plates 212 from the wafer S.
Meanwhile, in a procedure of the fabrication, normally, a frequency adjustment (rough adjustment) of the piezoelectric plate 212 is carried out before fragmentation. Specifically explaining, first, the pair of vibrating arm portions 210 are oscillated by applying a drive voltage by contacting terminals of a frequency adjustor (for example, an oscillating circuit, a network analyzer or the like) respectively to the pair of mount electrodes 214. Further, the weight of the weight metal film 215 is adjusted by a trimming apparatus (for example, laser or the like) of the frequency adjustor while measuring a frequency at this occasion by the frequency adjustor. Thereby, the frequency adjustment can be carried out.
However, in the above-described method of fabricating the piezoelectric vibrating piece, the following problem remains.
First, in order to carry out the frequency adjustment of the piezoelectric plate, it is necessary to contact terminals of the frequency adjustor to both of the pair of mount electrodes. That is, it is necessary to contact the two terminals to the one piezoelectric plate. However, the pair of mount electrodes are formed in a state of being aligned in parallel on an outer surface of the piezoelectric plate having a size of a width by about several hundreds μm. Therefore, in order to accurately carry out the contact, it is necessary that the two terminals are made to be proximate to each other as much as possible, thereafter, the two terminals are positioned to the pair of mount electrodes. Therefore, the control of the terminal is difficult, the positioning is obliged to be carried out with care. Therefore, time is taken for adjusting the frequency and an efficient operation cannot be carried out.
Further, in recent years, the size of the piezoelectric vibrating piece is downsized, and also an interval of a pair of mount electrodes is narrowed. Therefore, the above-described problem becomes significant. Further, in accordance with the downsizing, also the mount electrode per se is downsized. Therefore, an area of contacting the terminal in adjusting the frequency becomes small, and it is difficult to contact the terminal. Therefore, also with regard to the point, control of the terminal becomes difficult, which effects an influence on an operational efficiency.
Further, in order to carry out the frequency adjustment as efficiently as possible, in a background art, there is also carried out a method of carrying out the frequency measurement on a plurality of the piezoelectric plates by not adjusting the piezoelectric plates one by one but by contacting the two terminals simultaneously to the plurality of piezoelectric plates. For example, there is provided a method of dividing the plurality of piezoelectric plates connected to the wafer by a unit of a row and measuring frequencies for the respective divided rows. Thereby, the operational efficiency can be increased, however, on the contrary, it is necessary to increase a number of the terminals of the frequency adjustors twice as much as a number of the piezoelectric plates vibrated simultaneously. Therefore, it is necessary to prepare a number of the terminals beforehand, and a reduction in cost is difficult to achieve. Further, the control of the terminals is difficult even in contacting the two terminals accurately to the one piezoelectric plate as described above. In contrast thereto, when the frequency adjustment is carried out simultaneously, it is necessary to simultaneously and accurately contact a number of the terminals to the mount electrodes of the plurality of piezoelectric plates, and therefore, a further difficult operation is constituted.
In addition thereto, when downsizing the size of the piezoelectric vibrating piece is aimed at as described, the interval between the contiguous piezoelectric plates is further narrowed. Therefore, there is brought about a situation in which contacting the respective two terminals to the plurality of piezoelectric plates per se becomes severe.
Further, as the terminals of the frequency adjustor increases, a number of steps consumed in maintenance of the terminals is needed. Therefore, although the frequency adjusting operation can efficiently be carried out by simultaneously carrying out the frequency measurement for the plurality of piezoelectric plates, on the contrary, a deterioration in maintenance performance is brought about.